This project examines the role of cyclic AMP in the control of cell division. Steroid hormones initiate cell division in amphibian oocytes by causing a rapid transient drop in the level of the cyclic AMP. Our studies demonstrate this is due at least in part to inhibition of adenylate cyclase by progesterone. Also under investigation is the possibility that progesteron-induced increases in free calcium may activate calmodulin and calmodulin-dependent phosphodiesterase, thereby contributing to the decline in cyclic AMP seen with progesterone, which causes initiation of cell division in these cells. Additional work is aimed at identifying changes in phosphoproteins during the cyclic AMP decrease by polyacrylamide gel electrophoresis and autoradiography of 32P-labeled oocytes. Such altered phosphoproteins may be candidates for regulatory molecules that maintain the physiological arrest of the oocyte on prophase.